This invention relates to a control device for a Compact Disk (CD) reader focusing system using fuzzy logic, and more specifically relates to a control device adapted to detect and segregate a light beam reflected by the surface of the compact disk from an incident light beam to the surface.
The invention, particularly but not exclusively, relates to a focusing control device for a source of monochromatic light in an audio data processing system of a CD reader, and the description which follows will cover that field of application for convenience of explanation.
Each CD reader contains two primary systems: an audio data processing system and a control servo-system. A CD reader is shown schematically at 1 in FIG. 1. The CD reader 1 has a data input terminal IN, a servo-control output terminal O1, and first O2 and second O3 data output terminals.
An audio data processing system 2 is connected between the data input terminal IN and the data output terminals O2 and O3, and includes a series of a buffer 4, an error corrector 5, an interpolation-muting (or concealment) and demultiplexing circuit 6, a digital filter 7, D/A converters 8 and 8xe2x80x2, and analog output filters 9 and 9xe2x80x2.
The audio data processing system 2 also includes a storage device 10, such as a RAM, which is connected bi-directionally to the error corrector 5 and adapted to store the data during the audio data de-interleaving phase.
The input terminal IN of the CD reader 1 is connected to a series of a bit detection device 11, itself connected to the servo-control output terminal O1 via a control servo-system 3, and a demodulator 12. The CD reader 1 further includes a control/display subsystem 13 coupled to the demodulator 12 and to the buffer 4 of the audio data processing system 2. The control/display subsystem includes a series of a decoding block 14, a function controlling device 15, and a display 16.
The control servo-system 3 and the control/display subsystem 13 are to control the mechanical operations of the CD reader 1, including auto-tracking, auto-focus, and user""s interface functions.
The data reading system 2 uses a semiconductor laser, the light beam of which must be kept on focus for tracking Pit. A motor is used for turning the disk at a constant linear velocity, as well as to change its speed according to the position of the pickup on the surface of the compact disk. The information supplied in the data is used for establishing the appropriate rotational rate and keeping the output data stream constant.
Finally, the CD reader 1 includes a clock signal generator block 17, having its input connected to the output of the bit detection device 11 and including a clock signal regenerator 18 connected to an elementary clock signal generator 19 which may be provided with a piezo-electric crystal 20.
As said before, the optical system of the CD reader 1 employs a monochromatic light source, specifically an output laser 21 (FIG. 2), which requires stabilization since it is a basically regenerative device with a temperature tied to the level of the output.
Thus, in order to extract an audio data signal, the audio data processing system 2 should be capable of segregating the reflected light beam from the incident light beam. This separation can be obtained essentially in either of two manners, schematically illustrated by FIGS. 2A and 2B. In FIG. 2A, a half-mirror 22 directs the light beam reflected from a disk 23 onto a light sensor 24. This known system is not very efficient because some of the light is lost along the direct transmission path.
FIG. 2B illustrates the combined use of a polarizing prism 25 and a quarter-wave plate for segregating the incident light beam from the reflected beam, this combination improves the system performance.
Both systems shown in FIGS. 2A and 2B employ a focusing laser lens LF as a means to focus the light beam.
The frequency response of a CD audio channel and the amount of crosstalk are functions of the spot size, that is to say, they are basic variables tied to the device optics.
The performance of a CD reader 1 is dependent on the detection and focusing of the light beam on the informational layer of a compact disk.
Devices effective to keep under control the system response to disturbance of large amplitude, by means of an algorithm based on binary logic, have been known, but such devices are complicated and low in efficiency.
Therefore, a major problem of the prior art CD readers is that the focusing systems cannot adequately control the system response to a disturbance of large amplitude in a simple and efficient manner.
Presented is a focusing system controller for a Compact Disk reader that uses fuzzy logic to control a focus error signal, and for driving a focusing servo-system of the Compact Disk reader to adjust the distance of the focal plane from the light beam reflected from the surface of the Compact Disk.
Embodiments of the invention can be practiced with other hardware devices without deviating from the inventive aspects. For instance embodiments can be adapted to work with Digital Video Disks (DVD). Further applications can be envisaged for a fuzzy controller used as herein in a Hard Disk (HD) or a Mini Disk (MD) control. Applications of this invention can extend to any system where a reading head must be kept within a given distance from another device to operate properly
The features and advantages of a controller according to the invention will be apparent from the following description of an embodiment thereof, given by way of non-limitative example with reference to the accompanying drawings.